This invention relates to combination locks of the type wherein a locking action is controlled by rotary elements such as sleeves with elongate peripheral teeth, one or more of which teeth is omitted on each sleeve. The teeth cooperate with blocking means which may comprise projections formed, for example, in a lock body adjacent the respective elements. The arrangement is such that when a tooth on any rotary element aligns with the respective blocking means, axial movement of the rotary elements, necessary to open the lock, is prevented; but when gaps in the rotary elements defined by the omitted teeth are brought into alignment with the blocking means, the gaps provide bypass means for the blocking means allowing the sleeves to be moved axially to open the lock.
One known lock of the above type is, for example, the padlock which is described in U.S. Pat. No.3,720,082 to Feinberg et al, issued Mar. 13, 1973. Here, the sleeves are carried in a lock casing on the longer leg of the lock shackle, and are coupled for rotation with surrounding combination dials via the peripheral teeth, which mesh with complementary teeth on the dials. When the gaps defined by the omitted teeth of the respective sleeves are brought into alignment with the blocking means, by rotation of the dials into their on-combination settings, the shackle can be drawn out of the casing to open the lock, with the sleeves moving axially in conjunction with the longer shackle leg, relative to the blocking means and relative to the dials. When, however, a tooth on any sleeve aligns with the adjacent blocking means (one or more of the dials having been moved away from the on-combination setting), outward movment of the shackle is prevented.
One problem which may arise in padlocks of the above type is that if a pulling force is applied to the shackle when it is locked, and each dial is selectively rotated, starting with the dial exhibiting the highest amount of friction, following this with the dial exhibiting the next highest amount of friction, et seq., it may in each case be possible to feel the engagement of the respective blocking means against the ends of the sleeve teeth, and also to feel in a manner akin to feeling a detent, when a gap comes into alignment with a blocking means. Thus, it may be possible to feel when each dial is brought into its on-combination setting so that it may, without prior knowledge, be possible to determine by feel the correct combination of the lock, thereby making the lock susceptible to being picked. Locks in accordance with the present invention are intended to reduce this possibility.